For some electrostatic printing processes, such as the MIDAX.RTM. process, it is necessary to dispense electrically conductive and magnetic toner. In conventional systems for doing this, there can be substantial problems associated with clumping of the toner. Also, it is difficult to reliably supply the toner to ensure that a sufficient amount is always available for the printing elements.
According to the present invention, an apparatus and method for ultimately supplying toner for electrostatic printing which minimize the possibility of clumping, enhance print quality and reduce edge dusting, utilize a minimum of moving parts, make printing set up easier, and reduce the time needed to make adjustments, are provided. Also according to the invention reliability is improved, as well as compatibility with magnetic color toner.
The basic supply of toner utilized in the practice of the invention is a fluidized bed. The mechanism for fluidizing the toner in the bed may be similar to that in Canadian published patent application 2059036, the disclosure of which is hereby incorporated by reference herein. However numerous changes need be made to properly supply the magnetic and conductive toner according to the invention, which is distinct from the non-magnetic and nonconductive toner set forth in the Canadian patent application.
The components of the apparatus according to the invention include a hopper assembly with two different dispenser blocks, each for mounting a bottle of toner, and for delivering the toner through a common chute into a container in which the toner is fluidized. The toner is dispensed from the bottles by supplying gas under pressure to a sintered stainless tube that extends upwardly into each of the bottles, one bottle being exhausted before controls automatically start dispensing toner from the second bottle, and indicator lights being provided to indicate when a bottle is being emptied. In the fluidized bed, the chances of the toner clumping are minimized, and the toner is withdrawn from the bed by a rotating external surface of a magnetized applicator roller. The applicator roller rotates in association with a metering blade to control the amount of toner that is removed with the roller. If poor imaging in one area of the electrostatic printing apparatus indicates a clump, a declumping procedure can be implemented.
According to one aspect of the present invention, a hopper assembly is provided for supplying toner to an electric printing apparatus. The assembly comprises: A first dispenser block comprising a body having a central passage, means for receiving an open end of a toner bottle in the central passage, a screen (e.g. 60 mesh) in the central passage adjacent the toner bottle receiving means, and a gas permeable but toner substantially impermeable tube (e.g. of sintered stainless steel) extending through the toner bottle receiving means a significant distance past the block, so as to penetrate (into a bottle received by the toner bottle receiving means) a distance significant enough to effect fluidization of toner in the bottle to effect discharge thereof through the screen. Means for mounting the first dispenser block in association with an electrostatic printing apparatus. Means for connecting the tube to a source of gas under pressure. And, a passage exterior of the dispenser block for guiding toner from the screen to an electrostatic printing apparatus.
The assembly also preferably comprises a second dispenser block substantially identical to the first block, and also with associated mounting mechanisms and control means. The toner is typically supplied from the dispenser blocks through a chute with an acoustic sensor for sensing the level of toner in the bed.
According to another aspect of the present invention an electrostatic printing apparatus is provided which comprises the following elements: A supply of conductive magnetic toner. A container for a fluidized bed of conductive magnetic toner. Means for automatically replenishing toner withdrawn from the fluidized bed from the supply. Means for fluidizing the toner in the container. A single applicator roller adjacent the container, and having an external surface thereof which extends into the container, the applicator roller including magnetic elements. Means for rotating the applicator roller about a horizontal axis. And, a metering blade cooperating with the applicator roller external surface for metering the conductive magnetic toner on the external surface.
The rotating means for the electrostatic printing apparatus comprises a reversible electric motor, and a declumping apparatus effects reverse rotation of the applicator roller while bringing a scraping blade into contact with the applicator roller, while simultaneously applying a vacuum to it.
According to another aspect of the present invention a method of applying conductive and magnetic toner to an applicator roller having magnets therein (an internal magnetic member) is provided. The method comprises the steps of: (a) Supplying powdered conductive magnetic toner to a container to maintain a predetermined level therein. (b) Maintaining the powdered toner in a fluidized bed in the container. And, (c) moving a non-magnetic rotating surface into operative association with the magnetic toner in the fluidized bed to collect toner thereon in the presence of magnetic fields from an internal magnetic member and remove it from the fluidized bed.
Step (a) is preferably practiced pneumatically, by fluidizing the powdered toner so that it will pass through a screen (e.g. a 60 mesh screen), and step (b) is practiced by passing fluidizing gas through a substantially horizontal sintered metal surface.
The invention also includes as another aspect thereof a method of declumping toner associated with an applicator roller having an external surface, of an electrostatic printer, which roller normally rotates in a first direction. The method comprises the steps of: (a) Temporarily reversing the direction of rotation of the applicator roller so that it rotates in a second direction opposite the first direction. And, (b) while practicing step (a), automatically scraping the exterior surface of the applicator roller while simultaneously applying vacuum thereto, to remove toner from the exterior surface. Steps (a) and (b) are preferably practiced for a time period of about 3-10 seconds (e.g. 4 to 5 seconds) by manually depressing an element which engages a microswitch which changes the direction of rotation of the roller, while bringing a scraping blade into contact with the external surface of the roller, and bringing a high level vacuum into close proximity thereto.
It is the primary object of the present invention to effect simplified, reliable, and practical supply of conductive and magnetic toner to an electrostatic printing apparatus. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.